Fatal attractions between otherwise normal proteins seem to be a common theme in Alzheimer’s disease (AD) and a diverse group of disorders related to AD. National Institute on Aging (NIA)-supported researchers at the University of Pennsylvania Alzheimer’s Disease Center (ADC) are interested in abnormal protein interactions in AD and related dementias. According to two researchers at this ADC, Drs. John Q. Trojanowski and Virginia M.-Y. Lee, “These proteins are attracted to each other through positive and negative charges. They then stick together and cause toxic lesions (see Key Terms) to form. That is, the proteins get all bunched up together, fatally injuring the cell.”
These researchers are looking at Lewy bodies (LBs) and their relationship to AD. LBs are a hallmark of Parkinson’s disease (PD). Recently, scientists identified LBs in the brains of patients with standard AD features (amyloid plaques and neurofibrillary tangles). In addition, LBs have been found in the brains of patients with AD-like dementia, but with sparse or no signs of AD pathology. These types of disorders with LBs collectively are called “dementia with Lewy bodies” (DLB).
Dr. Kenji Kosaka first described DLB in 1978. Several research groups in the United States and United Kingdom have reported DLB as the second most common form of dementia in older people, next to AD.
How and why LBs and AD develop are unknown. Researchers now are able to identify LBs under a microscope, but their exact makeup and role in AD remain unclear. To answer these questions, Drs. Trojanowski and Lee are studying abnormal protein buildup and neuron death in PD and DLB.
These and other scientists have found that abnormal protein interactions cause protein filaments to form and build up; this is called filament accumulation. These toxic brain lesions are a common feature of some sporadic and hereditary dementias. Such interactions may play a role in the development of amyloid plaques and neurofibrillary tangles, which are characteristic of both sporadic and familial AD. These same interactions also may play a role in the formation of prion protein deposits found in the brains of patients with sporadic and genetic spongiform encephalopathy.
According to Dr. Trojanowski, “We want to draw attention to parallels among the lesions you find in AD, PD, prion disease, tauopathies, and other diseases. Some lesions are outside cells (extracellular) and others are inside (intracytoplasmic), but the central theme is filament accumulation. Another parallel is that these lesions are created from proteins, such as alpha-synuclein, but not the same protein in each disease. They all start out as normal (healthy functioning) proteins that, for some unknown reason, change from being soluble to insoluble or from good to bad.”
Source: Connections Magazine [Volume 7(2), Fall 1998]